The present invention relates generally to a control system for a fuel pump in a fuel supply system of an internal combustion chamber. More particularly, the invention relates to a fuel pump control system for controlling fuel pressure in a fuel supply system in accordance with the engine operating conditions.
In general, a fuel pump for a fuel supply system of an internal combustion engine, such as a gasoline engine, is provided in a fuel supply circuit to draw fuel out of a fuel tank and drive same through the fuel supply circuit at a certain pressure.
Published Japanese Patent Application (Tokkai) Showa No. 54-163219, published on Dec. 25, 1979, discloses a fuel pressure control system which adjusts the voltage applied to a fuel pump depending upon the engine load. In the disclosed system, a limited voltage will be applied to the fuel pump under relatively low engine load conditions and a full voltage will be applied to the fuel pump under relatively high engine load conditions. Control of supply voltage is performed by a controller including a power transistor rendered conductive or nonconductive according to engine operating conditions, and a resistor connected in series to limit the supply voltage under low engine load conditions and disconnected to allow application of full voltage to the fuel pump under high engine load conditions.
In such a fuel pump control system, the controller is mounted in the front end of the passenger compartment or in the engine compartment. On the other hand, the fuel pump is mounted near the fuel tank which is in the rear end of the vehicle in most cases. As a result, the wiring connecting the controller and fuel pump is so long that the supply voltage may drop significantly. This causes a lack of power of the fuel pump during engine start-up under a demand for sudden acceleration, which in turn causes a leaner air/fuel mixture than required. Furthermore, the lack of fuel pressure increases the probability of vapor-lock in the fuel supply system under relatively high temperature conditions.
The present invention is intended to improve the prior system by directly connecting a vehicle battery to the fuel pump under certain conditions to ensure sufficient supply voltage for the pump.